If you just want to quickly customise the form layout use this bookmarklet below. Don’t add any new fields from this window, as it will create the field with the Default Publisher’s prefix, which by default is “new_”.

Unminified

var entityName = prompt("Entity?", "");
var url = Xrm.Page.context.getClientUrl() + '/main.aspx?etn=' + entityName + '&extraqs=formtype%3dmain&pagetype=formeditor';
window.open(url, '_blank');

Minified

javascript:var%20entityName=prompt("Entity?","");var%20url=Xrm.Page.context.getClientUrl()+'/main.aspx?etn='+entityName+'&extraqs=formtype%3dmain&pagetype=formeditor';window.open(url,'_blank');void%200;

If you just want to quickly refresh all the subgrids in the form, without refreshing the whole page, use this bookmarklet.

Unminified

(function () {
	var contentPanels = Array.from(document.querySelectorAll('iframe')).filter(function (d) {
			return d.style.visibility !== 'hidden'
		});
	if (contentPanels && contentPanels.length > 0) {
		var Xrm = contentPanels[0].contentWindow.Xrm;
		Xrm.Page.ui.controls.forEach(function (c) {
			if (c.getControlType() === 'subgrid') {
				c.refresh();
			}
		});
	} else {
		alert('Entity form not detected');
	}
})();

Minified

javascript:(function(){var%20contentPanels=Array.from(document.querySelectorAll('iframe')).filter(function(d){return%20d.style.visibility!=='hidden'});if(contentPanels&&contentPanels.length>0){var%20Xrm=contentPanels[0].contentWindow.Xrm;Xrm.Page.ui.controls.forEach(function(c){if(c.getControlType()==='subgrid'){c.refresh();}});}else{alert('Entity%20form%20not%20detected');}})();void%200;